sim file parser and generator

sim file parser and generator

The generator doesn't emit the best possible connect commands,
but it does output something valid. Eg, an input like:

connect A <-> B <-> C <-> D

becomes:

connect A <-> B <-> C
connect C <-> D

Also:

connect A -> B <- C

becomes:

connect A -> B
connect C -> B

Which could be improved.

Also disconnect commands are not prettified at all, but probably there's
no reason to.